Add support for builtins, and implement true/0, fail/0, call/1, and !/0 builtins

1 files changed, 92 insertions, 0 deletions

diff --git a/builtins.c b/builtins.c
new file mode 100644
index 0000000..5db5e62
--- /dev/null
+++ b/builtins.c
@@ -0,0 +1,92 @@
+#include <u.h>
+#include <libc.h>
+
+#include "dat.h"
+#include "fns.h"
+
+int builtintrue(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtinfail(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtincall(Term *, Term *, Goal **, Choicepoint **, Binding **);
+int builtincut(Term *, Term *, Goal **, Choicepoint **, Binding **);
+
+Builtin
+findbuiltin(Term *goal)
+{
+	int arity;
+	Rune *name;
+
+	switch(goal->tag){
+	case AtomTerm:
+		arity = 0;
+		name = goal->text;
+		break;
+	case CompoundTerm:
+		arity = goal->arity;
+		name = goal->text;
+		break;
+	default:
+		return nil;
+	}
+
+	if(!runestrcmp(name, L"true") && arity == 0)
+		return builtintrue;
+	if(!runestrcmp(name, L"fail") && arity == 0)
+		return builtinfail;
+	if(!runestrcmp(name, L"call") && arity == 1)
+		return builtincall;
+	if(!runestrcmp(name, L"!") && arity == 0)
+		return builtincut;
+
+	return nil;
+}
+
+int
+builtintrue(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goal);
+	USED(goals);
+	USED(choicestack);
+	USED(bindings);
+	return 1;
+}
+
+int
+builtinfail(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goal);
+	USED(goals);
+	USED(choicestack);
+	USED(bindings);
+	return 0;
+}
+
+int
+builtincall(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(choicestack);
+	USED(bindings);
+
+	Goal *g = malloc(sizeof(Goal));
+	g->goal = goal->children;
+	g->next = *goals;
+	*goals = g;
+
+	return 1;
+}
+
+int
+builtincut(Term *database, Term *goal, Goal **goals, Choicepoint **choicestack, Binding **bindings)
+{
+	USED(database);
+	USED(goals);
+	USED(bindings);
+
+	Choicepoint *cp = *choicestack;
+	while(cp != nil && cp->id == goal->clausenr)
+		cp = cp->next;
+	*choicestack = cp;
+	return 1;
+}
\ No newline at end of file